What is the actual difference between the weight and the mass of an object?

Weight and mass are related to each other, but not the same thing. When you step onto a weighing scale and it gives you a number (this could be in kilograms, or pounds, etc), this is your mass- it is telling you how much 'stuff' or matter you have inside you. Your mass will always stay the same (at a given point in time) regardless of where you are- you'd have exactly the same mass stood on the moon as you would have on earth. Weight is an example of a force, which is caused by gravity. As it is a force, weight is always measured in Newtons, which can be confusing as most people refer to their 'weight' in units of kilograms (i.e. I weighed 60 kg last week). Always remember this value is actually their mass- it is just a standard way of describing our mass that people have been using for years. We can use the equation weight= mass x gravitational field strength to work out a weight from a given mass, as long as we understand what gravitational field strength means. On Earth, you can easily calculate your weight by multiplying your mass by 10, and this is because the gravitational field strength on Earth is roughly 10 newtons per kilogram. Gravitational field strength is simply a measurement of how strong the effect of gravity is around a particular object. It tells us how much force (in newtons) is exerted per kilogram of our mass. If you were on the moon however this would not work! Since the moon is smaller, gravity is weaker there, with a gravitational field strength of only 1.6 N/Kg, about 6 times weaker. We would have to change this calculation and multiply by 1.6 instead of 10- meaning on the moon you have a much smaller weight. This is why astronauts can make such long and high jumps on the moon, because their weight is not pulling them back down to the moon quite as strongly as it would on Earth.

Answered by Amy S. Physics tutor


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